Answer
$17936135$
Work Step by Step
The general formula to find the sum of a finite geometric sequence is given as: $ S_{n}=\dfrac{a_1(1-r^n)}{1-r}$
Here, $ a_1=5$ and $ r=-3$
Plug $ n=15$
$ S_{n}=\dfrac{a_1(1-r^n)}{1-r}$
Now, $ S_{15}=\dfrac{(-5) \times (1-(-3)^n)}{1-(-3)}=17936135$
